An axial gas turbine comprises a compressor section, a combustor section and a turbine section. In the compressor section, combustion air is compressed, and this compressed combustion air is then mixed and burned with fuel in the combustion section, forming a hot working gas. The hot gas which is formed is passed through a hot-gas duct in the turbine section. Guide vane rings and rotor blade rings or ring segments are arranged alternately in the turbine section. Flow path components comprising guide vanes and rotor blades are arranged adjacent to one another in the circumferential direction in each of these blade/vane rings.
The temperatures in an axial flow gas turbine reach levels which may exceed the melting points of the materials that are used for the components of the engine and/or reduce the hot strength of the materials to an unacceptable extent. For this reason, the components in the hot-gas duct are often cooled with a cooling medium. For example, air is generally branched off from the compressor to act as a cooling fluid to the turbine section components. The demand for cooling drops along the axial direction of flow in the hot-gas duct. Hence, cooling air at a lower pressure level than cooling air for front turbine stages is sufficient to cool rear turbine stages. To minimize the consumption of cooling air, since it reduces the efficiency of the gas turbine, the axially different turbine stages, i.e. the different blade/vane rings, are acted on by cooling air from different pressure levels. Thus, blade/vane rings which higher pressure than blade/vane rings lying further downstream in the direction of flow.
In view of the different supply pressures of cooling air to the adjacent blade/vane rings, it is desirable to form a seal between the different pressure levels in the axial direction. A seal is also desirable in order to prevent hot gas from being mixed into the cooling air and therefore to preserve the effectiveness of the cooling air.